This invention relates to an automatic program selector for a record player and, more particularly, to an electronic program selector which is particularly adapted for use in a record player of the type having a turntable which is driven into and out of a protective housing.
In a typical phonograph record of the so-called long-playing type, a multiple of selections, or programs are recorded in a surface of the record disc. Each program is recorded in a spiral groove, referred to as a sound groove, having undulations representing sound signals, which sound signals are sensed by a stylus which rides in the groove and which vibrates in response to such undulations. Typically, the selections, or programs, are spaced from each other by gaps on the record, which gaps are substantially free of sound grooves. Hence, at the completion of one program, the stylus, which is supported by a tone arm, advances through the gap to the next-following program, and this next program then is played back.
In record players that are not provided with automatic program selector apparatus, any desired program may be played back merely by having the user lift the tone arm from the surface of the disc and advance, or move that tone arm to a desired program which is identified by the usual record information label which indicates the particular gap that precedes the desired program. This, of course, requires the user to count the gaps until the proper gap is located.
In an effort to provide automatic program selector apparatus, record players have been designed with selector switches, each switch being associated with a respective gap, and the desired program is played back by actuating the proper switch so as to drive the tone arm automatically to the selected gap. In one type of program selector, a sensor is provided for sensing the presence and absence of the usual sound groove, thereby detecting the location of each inter-program gap (i.e. the gap which separates adjacent programs). Typically, the sensor is disposed in the same pick-up cartridge that houses the stylus and pick-up coil. In order to accommodate the sensor, the physical size of the cartridge must be sufficiently large or, alternatively, the so-called "head shell" which supports the cartridge must be made relatively large. In addition to housing the sensor, the cartridge or head shell also must accommodate the necessary electrical terminals and conductors which electrically interconnect the sensor to control electronics. Because of this large size of the cartridge, it is not readily interchangeable with conventional, commercially available cartridges. Hence, the user who periodically replaces the cartridge because of normal wear is limited as to available replacements. This increases the usual maintenance cost associated with the record player.
In order to provide automatic program selector apparatus that is usable with conventional, readily available record player cartridges, a relatively complicated mechanical arrangement has been proposed in order to sense the locations of the inter-program gaps on the record. For example, in one type of mechanical arrangement, a pivotable sensor arm is provided, independently of the tone arm, and is adapted to move, or scan, across the surface of the record. The sensor arm is provided with a sensor for sensing each location of the inter-program gap as the sensor arm scans the record. Since the surface of the record exhibits different reflectivity coefficients at those portions containing sound grooves and those portions which are free of such sound grooves (i.e. the inter-program gap), the sensor may comprise a photodetector which detects this change in reflectivity so as to sense each inter-program gap. As an example, the photodetector may comprise a light source for directing a light beam onto the surface of the record disc and an optical detector for detecting the intensity of the reflected beam. An increase in intensity due to the reflection of the beam from the inter-program gap is sensed to identify the location of that gap.
The aforedescribed sensor arm also is provided with a mechanism by which the relative position thereof with respect to the record is indicated. For example, a counter mechanism may be provided, the count of the counter mechanism being incremented as the sensor arm scans the record. Thus, the count of the counter mechanism represents the relative position of the sensor arm with respect to the record. As one example of the counting mechanism, an index or scale, such as a grid having indicia thereon, cooperates with a pick-up device for sensing the indicia, whereby each sensed indicium increments the count of a counter. The pick-up device may comprise a photo-detector or, alternatively, if the indicia is formed of discrete magnetic elements, the pick-up device may comprise a conventional magnetic detector.
As the sensor arm scans the record, the aforementioned counter produces a count which represents the relative position of that arm with respect to the record. A suitable storage device is provided with the instantaneous count of the counter whenever an inter-program gap is sensed. Thus, the relative locations of each inter-program gap are stored.
After the sensor arm is driven to scan the record, a program selector switch is operated to initiate a similar scanning operation of the tone arm. The tone arm is coupled to a counting mechanism similar to that provided on the sensor arm so as to provide an indication of the relative location of the tone arm as it scans across the record. When the tone arm count corresponds to the selected sensor arm count, thus representing that the relative position of the tone arm is equal to the selected location of the desired inter-program gap, the tone arm drive mechanism then drives the tone arm into engagement with the record so as to play back the program which follows the selected inter-program gap.
The aforedescribed program selector apparatus which employs the separate sensor arm is relatively complicated and, thus, substantially increases the cost of the record player with which it is used. Furthermore, a selected program cannot be played back until after the sensor arm completes its scan of the record. This delay in playing back the selected program is undesirable.